Radiation-impermeable composite materials make it easier to detect marginal deficit or decayed teeth in the tooth tissue adjacent to the hardened composite material when examined with a standard X-ray unit for dental use.
The composite materials for dental use are required to have such characteristics as strength, hardness, and smoothness equivalent to those of a natural tooth, resistance against wearing caused by toothing, compatibility in color tone to natural teeth, appropriate refractive index giving the transparency equivalent to that of natural teeth, and x-ray impermeability which can be differentiated from that of natural teeth. Further it is required that the composite materials can easily be machined.
As the composite material for dental use, for instance, a radiation impermeable composite material for dental use comprising a polymeric resin and non-vitreous micro particles (comprising a homogeneously distributed polycrystalline metal oxide and non-crystalline silicon oxide(s)) is disclosed in Japanese Patent Laid-Open Publication No. SHO 60-233007. In this composite material for dental use, the non-vitreous micro particles contain polycrystalline metal oxides, so that the composite material does not have the transparency equivalent to that of natural teeth. Further when the composite material is heated at a temperature lower than the crystallizing temperature to obtain transparency, strength of the particles becomes insufficient, so that the strength of a tooth repaired with the composite material becomes lower and also the hardness and resistance against wearing caused by toothing sometimes become insufficient.
Japanese Patent Laid-Open Publication No. HEI 7-196428 discloses a non crystalline filler for composite materials for dental use manufactured by aggregating silicon dioxide and other metal oxide(s) and heating the aggregate at a temperature lower than the crystallizing temperature of the metal oxide. This filler (particles) is manufactured by aggregating silicon dioxide and other metal oxide(s), so that the pore volume and strength of the particles can not be controlled, and therefore the transparency can not be improved, or as the adhesiveness thereof to a polymeric resin is not enough, the strength of a tooth repaired with the material becomes lower, and sometimes the hardness and resistance against wearing caused by toothing may be insufficient.